1. Field of the Invention
The present invention relates to a method for manufacturing an electron source using electron-emitting devices and, more particularly, to an activation procedure of the electron source.
2. Related Background Art
Heretofore, there have been self light-emitting type image-forming apparatuses such as plasma display, EL display apparatus and image-forming apparatus using an electron beam. Currently, there is increasing a demand for a large-sized screen and high definition, so that need for the self light-emitting type image-forming apparatus is increasing.
As a self light-emitting type image-forming apparatus using, for example, an electron beam, a thin type image-forming apparatus using electron-emitting devices as an electron source for generating an electron beam in a vacuum envelope constructed by a face plate, a rear plate, and an external frame, for accelerating the electron beam and irradiating the beam onto phosphor to emit light, thereby displaying images has been filed by the same applicant as the present invention (JP-A-7-235255).
Since the structure of the above electron-emitting device is simple and the manufacture is easy and the devices can be arranged in array on a large-sized substrate, the electron source is suitable for a large-sized image-forming apparatus. The same applicant as the present invention has disclosed the fundamental structure and manufacturing process of the electron-emitting device and a method for manufacturing an image-forming apparatus using the electron-emitting devices in JP-A-7-235255.
In addition to the electron-emitting device, there are known electron source such as thermionic source using thermionic cathodes, electron-emitting device of a field emission type (W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical properties of thin film field emission cathodes with molybdenum conesxe2x80x9d J. Appl. Phys., 47, 5248 (1976)), and metal/insulator/metal type electron-emitting device (C. A. Mead, xe2x80x9cThe tunnel emission amplifierxe2x80x9d, J. Appl. Phys., 32, 646 (1961)).
As an example of the electron-emitting device type, there is one disclosed by M. I. Elinson, Recio Eng. Electron Phys., 10, 1290, (1965).
The electron-emitting device utilizes a phenomenon that an electron emission is produced in a small-area thin film formed on a substrate by supplying a current in parallel with the film surface. As electron-emitting devices, electron-emitting devices using an SnO2 thin film according to Elinson mentioned above, devices using an Au thin film (G. Dittmer: xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972)), devices using an In2O3/SnO2 thin film (M. Hartwell and C. G. Fonstad: xe2x80x9cIEEE Trans. Ed Conf.xe2x80x9d, 519 (1975)), and devices using a carbon thin film (Hisashi Araki et al.: xe2x80x9cVacuumxe2x80x9d, vol.26, No.1, p.22 (1983)) have been reported.
A construction of the above-mentioned device according to M. Hartwell is schematically shown as a typical example of those electron-emitting devices in FIG. 19. FIG. 19 is a schematic diagram showing an example of the surface conduction type electron-emitting device as a related art.
Referring to FIG. 19, reference numeral 1 denotes a substrate; and 4 an electroconductive thin film made of metal oxide by sputtering, being formed in an H-shaped pattern. An electron-emitting region 5 is formed in the thin film by an energization operation called xe2x80x9cenergization formingxe2x80x9d which will be described hereinlater. In FIG. 19, a device electrode interval L is set to 0.5 to 1 mm and a width Wxe2x80x2 is set to 0.1 mm.
Hitherto, in the electron-emitting device, the electron-emitting region 5 is generally formed by previously performing the energization operation called xe2x80x9cenergization formingxe2x80x9d to the electroconductive thin film 4 before the electron emission. In other words, in the energization forming, energization is made by applying a direct current voltage or a voltage that increases at a very slow rate of, for example, 1V/min to both ends of the electroconductive thin film 4 so as to partially destroy or deform the electroconductive thin film, or change in properties of the film, so that the electron-emitting region 5 in an electrically high-resistant state is formed. A fissure is partially formed in the electroconductive thin film 4 by the energization forming. In the electron-emitting device to which the energization forming operation has been performed, the voltage is applied to the electroconductive thin film 4 to supply the current through the device, so that electrons are emitted near the fissure in the electron-emitting region 5.
The present applicant has proposed an image-forming apparatus constructed by combining an electron source in which a large number of the above-mentioned electron-emitting devices are arranged and phosphor which emits visible light due to the electrons emitted from the electron source (U.S. Pat. No. 5,066,883).
The present applicant has proposed that upon manufacturing the above-mentioned electron source and image-forming apparatus, a new process referred to as an activation operation (to be described in detail hereinlater) is performed to the foregoing electron-emitting devices, the activation procedure controls to form a film constituted of graphite, amorphous carbon, or mixture of them, containing carbon as a main component, near the electron-emitting region of the electron-emitting device, so that an emission current from each electron-emitting device can be increased in a vacuum.
The activation procedure is an operation which is performed to the electron-emitting devices after completion of the forming operation and which enables the emission current from the devices to be remarkably increased by repeating the application of a predetermined pulse voltage in an environment at a degree of vacuum of substantially 1xc3x9710xe2x88x924 to 1xc3x9710xe2x88x925 Torr. FIG. 4 shows an example of a pulse voltage waveform upon activation operation and FIG. 5 shows an example of time change in device current If and emission current Ie running through the electron-emitting devices upon activation operation.
Executing the activation operation results in an increase of the emission current Ie of the electron-emitting devices, so that the performance of the electron source utilizing the devices and image-forming apparatus can be improved.
The above-mentioned activation procedure is utilized to increase the emission current Ie. In the image-forming apparatus having the electron source comprising a plurality of electron-emitting devices in a vacuum container, however, realization of a large size is desired in recent years, the number of electron-emitting devices used in the electron source is extremely increased in association with the enlargement, and the activation operation requires a long time in association with the increase, so that an increase of manufacturing costs becomes a problem.
The following method has been considered in order to solve the problems. First, an activation gas made of a predetermined chemical material is introduced to a vacuum container and, after that, a plurality of electron-emitting devices are divided into a plurality of blocks. Repetitively applying a predetermined pulse voltage to a plurality of electron-emitting devices belonging to one block at the same time allows the electron-emitting devices in the block to be activated and the activation of the block is terminated.
After that, the activation operation is subsequently executed to blocks which are not yet activated. The activation operation for blocks is sequentially continuously performed and the activation for all of the electron-emitting devices is terminated. At that time, the number of electron-emitting devices in each block is increased, so that the number of electron-emitting devices to be simultaneously activated is increased. Consequently, the necessary time for the activation operation for the whole electron source can be reduced. Accordingly, the manufacturing costs can be suppressed to a low price.
Since the vacuum container constructs the image-forming apparatus, the vacuum container is connected to a vacuum exhausting system in various vacuum processes including the activation process and, after completion of the vacuum process, the container is separated from the vacuum exhausting system and functions solely as an image-forming apparatus. Therefore, the container has a narrow cylindrical exhaust pipe made of glass for connection with the vacuum exhausting system and it is necessary to introduce the activation gas to the vacuum container through the exhaust pipe.
In the case where the activation operation for each block comprising the plurality of electron-emitting devices is continuously executed, however, when the large number of electron-emitting devices are simultaneously activated, the activation gas in the vacuum container is consumed for the activation operation for the large number of devices at the initial stage of the activation and the amount is reduced, so that there is such a problem that the activation gas pressure in the vacuum container is fluctuated until the introduction volume of the activation gas is equivalent to the consumption.
FIG. 20 shows an example. In FIG. 20, the axis of abscissa denotes time when the blocks are sequentially activated continuously and the axis of ordinate indicates the activation gas pressure in the vacuum container. FIG. 20 shows that the activation gas pressure fluctuates at the initial stage of the activation by continuously activating the blocks and, after that, the pressure is stabilized, namely, a stability region follows.
Consequently, the electron-emitting properties of the electron emitting devices which belong to the block activated initially in the activation procedure are different from those of the electron-emitting devices activated after that, so that there is caused such a problem that a variation in luminance of the image-forming apparatus is generated.
The above problem tends to occur more frequently as the image-forming apparatus increases in size and the number of electron-emitting devices which are simultaneously subjected to the activation operation increases. In future realization of the increase in size of the image-forming apparatus, it is beginning to be highlighted as a very serious problem.
The present invention is made in consideration of the above problems included in the related arts and it is an object of the present invention to provide a method for manufacturing an electron source in which a variation in luminance can be suppressed and activation operation time for the whole electron source comprising a large number of electron-emitting devices can be reduced.
According to the present invention, there is provided a method for manufacturing an electron source, including an activation operation for repetitively applying a pulse voltage to each of a plurality of electron-emitting devices in an atmosphere containing an organic material to form a film containing carbon from the organic material existing in the atmosphere, wherein the activation operation for the plurality of electron-emitting devices is performed in such a manner that the activation operation is divided into a plurality of steps of first to final activation steps, the plurality of electron-emitting devices are divided into operation units each comprising a plurality of device groups, the first activation step of the activation operation is sequentially executed from an arbitrary operation unit, the first activation step for all of the operation units is terminated, after that, the plurality of electron-emitting devices are divided into operation units each comprising a plurality of device groups in a manner similar to the first activation step, the next activation step for all of the operation units is terminated, and such a procedure is repeated to execute up to the final activation step.
According to the present invention, there is provided a method for manufacturing an electron source, including an activation operation for repetitively applying a pulse voltage to each of a plurality of electron-emitting devices in an atmosphere containing an organic material to form a film containing carbon from the organic material existing in the atmosphere, wherein the activation operation is divided into a plurality of steps and then performed to the same electron-emitting device, the activation operation divided into the plurality of steps has a pause time during which the activation operation is not performed between the activation operation steps for the same electron emitting device, waveform conditions of the pulse voltage at the initial stage of the activation operation in the next step to be performed after the pause time are made different from those of the pulse voltage at the final stage of the activation operation in the preceding step.